Efforts have been underway recently to reduce power consumption in computers. Computers including desktop PCs and portable computers are prevalent in most everyday office and home life. While most PCs consume a modest amount of power, in combination they consume a significant amount of power. In addition, portable computers are constantly striving to reduce power consumption, which enables it to have prolonged times between recharging of a battery supply, and/or to have a smaller size battery.
In conjunction with power conservation efforts, capabilities of computers are expanding to include real time entertainment applications, e.g., such as audio, video, and game applications, as well as the more traditional computing applications. For instance, CD/DVD-ROM drives are becoming more commonplace in many computers. In addition to traditional uses, such drives enable a user to play standard music CDs on their computer equipped with appropriate audio transducers, e.g., speakers. For audio applications, MP3 files and MP3 players may also be used to listen to audio data. The DVD-ROM drive and associated video subsystems may also permit a user to view a video on the computer display screen. In addition, various video games may also be played.
Such real time applications are typically not compatible with typical PC and portable computer processor power conservation efforts. As opposed to other applications, real time applications require the computer system to be able to respond to any request at any time. Therefore, the computer's operating system maintains the processor in, at most, a light sleep state. If the processor were put into a deep sleep state, the processor may not be fast enough to keep up with the output data from the real time application. In the case of an audio application for instance, the user would hear a click sound. In the case of a video application, the video screen would be frozen for a short period of time.
In addition, most processors have cache memory to enhance processing power. In order to keep data coherency between cache memory and system memory, the processor has to keep track of access from any other components in the system. Some components may have direct access to system memory. For example, an audio component in an audio subsystem may be able to retrieve audio data directly from system memory.
To support such direct access methods, each component has to know when it needs more data and where to retrieve it. With a processor having an internal cache memory, some of the data may be temporarily stored in cache memory rather than system memory. Because of this the processor cannot be put into a deep sleep mode when any of the system components use such direct access methods. Accordingly, power conservation efforts in these instances are thwarted.
Finally, components that are connected to the same bus must be in the same or lower power state as the bus itself. This protocol is supported by the Advanced Configuration and Power Interface (ACPI) Specification, which is a Specification jointly established by Intel Corporation, Microsoft Corporation, and Toshiba Corporation in order to facilitate controlling electrical power consumption in computers. However, this protocol presents power conversation limitations. One example utilizing this protocol is listed in PCI Bus Power Management Interface Specification Revision 1.1.
For instance, if the component is a real time application component, e.g., an audio or video component, that needs to be in a higher power state in order to perform certain operations, e.g., video or audio playback, the connected bus in such a computer system would have to be in a similar higher power state. In addition, some other components may also have to be in the same or higher power state in order to maintain the bus in the higher power state. This ends up increasing power consumption of the entire computer.
Accordingly, there is a need for an apparatus and method that overcomes the above deficiencies in the prior art to allow for improvements in power conservation techniques including an apparatus capable of allowing a processor and other system components to enter a deep sleep power state while playing real time applications without degradation in audio and video output performance.